refactor(gc): remove format_stats

Review decision: format_stats presumed a single display format and was never
called by the library — scan()/collect() return plain dicts. Users inspect or
render those dicts however they like, so the helper only added surface area.
Removed the function and its three unit tests. GC suite 36/36.

Docs that showed dj.gc.format_stats(stats) are updated to inspect the stats
dict directly (datajoint-docs).

Author: dimitri-yatsenko

src/datajoint/gc.py

@@ -709,71 +709,3 @@ def collect(
         "hash_orphaned": stats["hash_orphaned"],
         "schema_paths_orphaned": stats["schema_paths_orphaned"],
     }
-
-
-def format_stats(stats: dict[str, Any]) -> str:
-    """
-    Format GC statistics as a human-readable string.
-
-    Parameters
-    ----------
-    stats : dict[str, Any]
-        Statistics dict from scan() or collect().
-
-    Returns
-    -------
-    str
-        Formatted string.
-    """
-    lines = ["Object Storage Statistics:"]
-
-    # Show hash-addressed storage stats if present
-    if "hash_referenced" in stats:
-        lines.append("")
-        lines.append("Hash-Addressed Storage (<hash@>, <blob@>, <attach@>):")
-        lines.append(f"  Referenced: {stats['hash_referenced']}")
-        lines.append(f"  Stored:     {stats['hash_stored']}")
-        lines.append(f"  Orphaned:   {stats['hash_orphaned']}")
-        if "hash_orphaned_bytes" in stats:
-            size_mb = stats["hash_orphaned_bytes"] / (1024 * 1024)
-            lines.append(f"  Orphaned size: {size_mb:.2f} MB")
-
-    # Show schema-addressed storage stats if present
-    if "schema_paths_referenced" in stats:
-        lines.append("")
-        lines.append("Schema-Addressed Storage (<object@>, <npy@>):")
-        lines.append(f"  Referenced: {stats['schema_paths_referenced']}")
-        lines.append(f"  Stored:     {stats['schema_paths_stored']}")
-        lines.append(f"  Orphaned:   {stats['schema_paths_orphaned']}")
-        if "schema_paths_orphaned_bytes" in stats:
-            size_mb = stats["schema_paths_orphaned_bytes"] / (1024 * 1024)
-            lines.append(f"  Orphaned size: {size_mb:.2f} MB")
-
-    # Show totals
-    lines.append("")
-    lines.append("Totals:")
-    lines.append(f"  Referenced in database: {stats['referenced']}")
-    lines.append(f"  Stored in backend:      {stats['stored']}")
-    lines.append(f"  Orphaned (unreferenced): {stats['orphaned']}")
-
-    if "orphaned_bytes" in stats:
-        size_mb = stats["orphaned_bytes"] / (1024 * 1024)
-        lines.append(f"  Orphaned size:          {size_mb:.2f} MB")
-
-    # Show deletion results if this is from collect()
-    if "deleted" in stats:
-        lines.append("")
-        if stats.get("dry_run", True):
-            lines.append("  [DRY RUN - no changes made]")
-        else:
-            lines.append(f"  Deleted:     {stats['deleted']}")
-            if "hash_deleted" in stats:
-                lines.append(f"    Hash items:   {stats['hash_deleted']}")
-            if "schema_paths_deleted" in stats:
-                lines.append(f"    Schema paths: {stats['schema_paths_deleted']}")
-            freed_mb = stats["bytes_freed"] / (1024 * 1024)
-            lines.append(f"  Bytes freed: {freed_mb:.2f} MB")
-            if stats.get("errors", 0) > 0:
-                lines.append(f"  Errors:      {stats['errors']}")
-
-    return "\n".join(lines)

tests/integration/test_gc.py

@@ -331,74 +331,6 @@ def test_deletes_orphaned_schemas(self, mock_scan, mock_list_schemas, mock_delet
         mock_delete.assert_called_once_with("schema/table/pk/field", "test_store", config=mock_schema.connection._config)
 
 
-class TestFormatStats:
-    """Tests for format_stats function."""
-
-    def test_formats_scan_stats(self):
-        """Test formatting scan statistics."""
-        stats = {
-            "referenced": 10,
-            "stored": 15,
-            "orphaned": 5,
-            "orphaned_bytes": 1024 * 1024,  # 1 MB
-            "hash_referenced": 6,
-            "hash_stored": 8,
-            "hash_orphaned": 2,
-            "hash_orphaned_bytes": 512 * 1024,
-            "schema_paths_referenced": 4,
-            "schema_paths_stored": 7,
-            "schema_paths_orphaned": 3,
-            "schema_paths_orphaned_bytes": 512 * 1024,
-        }
-
-        result = gc.format_stats(stats)
-
-        assert "Referenced in database: 10" in result
-        assert "Stored in backend:      15" in result
-        assert "Orphaned (unreferenced): 5" in result
-        assert "1.00 MB" in result
-        # Check for detailed sections
-        assert "Hash-Addressed Storage" in result
-        assert "Schema-Addressed Storage" in result
-
-    def test_formats_collect_stats_dry_run(self):
-        """Test formatting collect statistics with dry_run."""
-        stats = {
-            "referenced": 10,
-            "stored": 15,
-            "orphaned": 5,
-            "deleted": 0,
-            "bytes_freed": 0,
-            "dry_run": True,
-        }
-
-        result = gc.format_stats(stats)
-
-        assert "DRY RUN" in result
-
-    def test_formats_collect_stats_actual(self):
-        """Test formatting collect statistics after actual deletion."""
-        stats = {
-            "referenced": 10,
-            "stored": 15,
-            "orphaned": 5,
-            "deleted": 3,
-            "hash_deleted": 2,
-            "schema_paths_deleted": 1,
-            "bytes_freed": 2 * 1024 * 1024,  # 2 MB
-            "errors": 2,
-            "dry_run": False,
-        }
-
-        result = gc.format_stats(stats)
-
-        assert "Deleted:     3" in result
-        assert "Hash items:   2" in result
-        assert "Schema paths: 1" in result
-        assert "2.00 MB" in result
-        assert "Errors:      2" in result
-
-
 class TestScanWithLiveData:
     """End-to-end tests for gc.scan() against real schemas with external storage.